Gastrointestinal smooth muscles adapt contractile activities in response to continuously changing conditions. Mechanical plasticity, such as hypertrophy, alters the functional capacity of smooth muscles in response to changing demands by reorganizing contractile bundles. The amplitude and frequency of cytosolic Ca 2+ oscillations encodes information that is translated into physiological responses. CaM kinase II has the structural, catalytic, and regulatory properties required of a molecular decoder of Ca 2+ oscillations. Fundus and colon smooth muscles, which exhibit distinct Ca 2+ oscillations, express CaM kinase II holoenzymes with tissue-specific enzymatic properties. In situ hybridization, kinase assays, Western blotting, and ratiometric Ca 2+ imaging will be used to investigate how CaM kinase II responds to cytosolic Ca 2+ transients in order to understand how it modulates smooth muscle contractile activity. Hypertrophy of gastrointestinal smooth muscles due to obstructions of the digestive tract resulting from congenital or acquired defects is associated with pathologies that lead to several motility disorders. Part of the cell volume increase results from elevated transcription and expression of contractile proteins under the control of serum response factor. Serum response factor is activated by CaM kinase II phosphorylation. Fundus and colon smooth muscles express CaM kinase II splice variants containing a nuclear localization signal. Cellular fractionation, Western blotting, kinase assays, Q-PCR, phosphopeptide mapping, and expression proteomics will be used to elucidate the role of CaM kinase II in the activation of contractile protein gene transcription by serum response factor. Gastrointestinal smooth muscle hypertrophy is important in normal physiology and disease. This project will explore the regulation and physiological roles of CaM kinase II in normal agonist-stimulated, and abnormal hypertrophied gastrointestinal smooth muscles. Determining the enzymatic characteristics of gastrointestinal smooth muscle CaM kinase II and investigating the modulation of gastrointestinal smooth muscle contraction by CaM kinase II will provide additional information for developing better therapeutics aimed at treating the myogenic component of the altered motility patterns that underlie digestive tract motility disorders.